For the audio drivers,
Latest Realtek HD Audio Driver Version
for the ethernet driver, that one I would just go with what Asus (or whoever made the motherboard). You can get them from Realtek, but that is one driver that doesn't see much in the way of updates anyway so just go with teh motherboard manufacturer for it.
You can alsways get them from Asus, but given that you know the board, you also know what hardware it has, so if you want to check for updates, you'll find them on the Realtek site. Assuming you know your hardware (which you should, since you can go to Asus's website and see it, including model numbers of the Realtek parts), you can easily find them from Realtek, too.
In some cases, the base Realtek driver doesn't include all apps or configs that the mobo makers put on their boards, so for audio, I'd stick to getting the driver from Asus. For the NIC, the Realtek drivers are fine as well.
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